The pharmacological function and importance of calcium antagonists, or calcium channel blockers, is well known and has been extensively reported in the literature [see; e.g., P. D. Henry, "Comparative Pharmacology of Calcium Antagonists: Nifedipine, Verapamil and Diltiazem", The American Journal of Cardiology, 46, 1047-1058 (1980); K. H. Dangman, et al, "Effects of Nifedipine on Electrical Activity of Cardiac Cells", The American Journal of Cardiology, 46, 1061-1067 (1980); E. Braunwald, "Introduction: Calcium Channel Blockers", The American Journal of Cardiology, 46,1045 (1980); L. D. Hillis, "The New Coronary Vasodilators: Calcium Blockers", J. Card. Med., 5(6), 583 (1980); M. J. Berridge, "Receptors and Calcium Signalling", Trends in Pharmacological Sciences 1, 419, (1980); W. G. Nayler, et al, "Calcium Antagonists: definition and mode of action", Basic Research in Cardiology, 76, No. 1, 1-15 (1981)].
Non-acylated pyrimidines of the formula I below are disclosed by K. Folkers, et al, [J. Am. Chem. Soc., 54, 3751-8 (1932)]; and K. Folkers and T. Johnson [J. Am. Chem. Soc., 55, 3784-91 (1933)]; A. Ehsan and Karimulah [Pakistan J. Sci. Ind. Res., 10(1), 83-5 (1967) (c.f. CA 68:78231z)]; and, E. L. Khania, et al, [Khim. Farm. Zhurnal., 12(10), 72-4 (1978)]. Non-acylated tautomers of the pyrimidines of formula Ia below are disclosed by M. A. Elkasaby [Pakistan J. Sci. Ind. Res., 21(2), 58-61 (1978) (c.f. CA 90: 152115n)].